September 18th

American nuclear physicist Edwin Mattison McMillan was born on this day in 1907

McMillan and his colleagues discovered the elements neptunium (Np) and plutonium (Pu), the two elements following uranium (U) in the periodic table. Their names were inspired by the position of the planets in the solar system - Neptune is beyond Uranus and Pluto (before being declassified as a planet) is beyond Neptune.